1. Field of the Invention
The present invention relates to a V8 engine and an outboard motor including the V8 engine.
2. Description of the Related Art
V8 engines (eight-cylinder V engines) include a first bank of four cylinders and a second bank of four cylinders. The first bank and the second bank are disposed in a V shape. In V8 engines, firing is conducted eight times within a crank angle of 720 degrees. Therefore, when firing intervals are even, firing is conducted at intervals respectively corresponding to a crank angle of 90 degrees. When a cross-plane crankshaft is used, firing is conducted at uneven intervals in each of the first and second banks.
In the engines, exhaust valves are opened before pistons reach the bottom dead center in an exhaust process. At this time, a phenomenon called exhaust blowdown occurs. In the exhaust blowdown, burnt gas rushes out to an exhaust system due to high pressure in a cylinder.
When cylinders are respectively connected to a common exhaust pathway, high pressure attributed to the exhaust blowdown in a given cylinder is transferred to another cylinder via the exhaust pathway. Therefore, when two cylinders, in which firing is conducted in close sequence, are connected through the exhaust pathway, there is a possibility that the high pressure attributed to the exhaust blowdown in one cylinder interferes with exhaustion of the other cylinder.
To inhibit the exhaust interference described above, Japan Laid-open Patent Application Publication No. 2008-31897 discloses a construction in which cylinders are paired off and connected through four exhaust pathways such that firing is conducted in each pair of cylinders at an interval corresponding to a crank angle of 360 degrees. Moreover, the four exhaust pathways are joined and integrated into two exhaust pathways. With the above construction, exhaust interference is inhibited.